The present invention relates to an electrophotographing apparatus and a developing agent ejecting method which are used in a printer, a copying machine, a facsimile, or the like to which an electrophotographing technique is applied. More particularly, the invention relates to an electrophotographing apparatus and a developing agent ejecting method for efficiently ejecting a used developing agent from a developing device which is used for supplying the developing agent to develop an electrostatic latent image on a photosensitive drum.
Hitherto, in such a kind of electrophotographing apparatus known as a laser printer, while a photosensitive drum is rotated, the surface is uniformly charged by a pre-charging device, a laser beam is exposed and scanned onto the surface of the drum, an electrostatic latent image of a pattern according to print information is formed, and the electrostatic latent image is developed by using a developing agent which is supplied by a developing device, thereby obtaining a toner image. On the other hand, a paper is fed from a hopper to a transfer position of the photosensitive drum and the toner image on the photosensitive drum is transferred onto the paper by a transfer charging device. After that, the toner on the paper is fixed by heat, pressure, light, or the like by a fixing device. As for the residual toner left on the photosensitive drum after the transfer, charges are eliminated by an AC discharging device and, after that, the residual toner is mechanically removed by a cleaning unit. Further, after executing an LED deelectrification for returning an electric potential on the photosensitive drum to an initial state (0V), the photosensitive drum surface is uniformly charged again by the pre-charging device and a subsequent printing process follows.
In such a conventional electrophotographing apparatus, a two-component developing agent constructed by a toner component consisting of fine powder particles of a coloring resin and a fine magnetic material carrier component is widely used. The developing device has: a stirring device for stirring the two-component developing agent in a container of the developing agent, thereby frictionally charging the toner component and the magnetic material carrier component; and a magnet roller for forming a magnetic brush by adsorbing a part of the magnetic material carrier by a magnetic force. The toner component is supplied from an exchangeable toner vessel. The magnet roller is exposed at a position of a developing region which faces the photosensitive drum. The toner component is electrostatically adhered to the head of the magnetic brush adsorbed and formed around the magnet roller and is conveyed to the developing region on the photosensitive drum, so that an electrostatic latent image is developed. A development concentration of the electrostatic latent image on the photosensitive drum in this case depends on an amount of toner which is conveyed to the developing region. In order to uniform the development concentration, a length of head of the developing agent which is formed as a magnetic brush onto the magnet roller is restricted by a doctor blade. The developing agent in which the toner component is reduced by the development is scraped from the magnet roller by a scraper and is returned to the stirring device side. The toner corresponding to a consumed amount is supplemented by the stirring device and the concentration is returned to a specified toner concentration. The toner is again used for development. When the toner component is consumed during the use and the specified toner concentration cannot be assured, a toner vessel is exchanged.
In the conventional electrophotographing apparatus, when a predetermined number of papers are printed, the developing agent in the developing device is replaced. This is because the magnetism of the magnetic carrier of the developing agent drops by an aging change and a printing ability deteriorates. This is called a developing agent life. In order to replace the developing agent, it is necessary to eject the used developing agent from the developing device. Generally, an ejecting port in the bottom plate of the developing device is opened, the magnet roller and a stirring screw are operated, and the developing agent in the developing device is completely ejected. In the case where the electrophotographing apparatus of this kind is used in a printing apparatus of a computer system, when the developing agent reaches the developing agent life during the operation of the system and a replacement of the developing agent is requested, since the developing agent is replaced in a state where the printing process is interrupted, it is requested to completely eject the developing agent in a short time. If the developing agent is not completely ejected in this instance, the developing agent in the developing device becomes too much after the replacement. A drive load of the developing device increases, so that the developing device cannot be driven or the developing agent overflows from the vessel. Further, when the toner concentration is controlled by using a magnetic permeability sensor, there is a problem such that the toner concentration is largely deviated from the specified value and is shifted to the high side, or the like. Consequently, in order to eject the developing agent completely, an ejecting work is certainly executed by taking a certain extent of time. In case of ejecting the developing agent by driving the magnet roller and stirring screw, for a predetermined period of time after the start of the ejection of the developing agent from the casing of the developing device, a large amount of developing agent is conveyed to a developing agent ejecting port by the stirring screw. When an amount of developing agent in the developing device decreases to a predetermined amount or less, the amount of developing agent is gradually reduced. In order to smoothly lead a large amount of developing agent for the predetermined period of time from the start of the ejection to a collecting vessel on the outside of the apparatus, a cross-sectional area of a minimum channel of a funnel provided at the ejecting port and a cross-sectional area of a channel of a hose have to be set to predetermined values or more, so that there is a certain limit when the apparatus is miniaturized. In recent years, not only the miniaturization of the apparatus but also the realization of an advanced function and a multi-function are strongly requested. With respect to a structure which is not usually used and is used for ejecting the developing agent, a miniaturization is also strongly requested, so that it is tried to use a small funnel and a small hose. If the small funnel is used, however, when a large amount of developing agent is dropped, the developing agent causes a bridge phenomenon and clogs in the funnel. When the hose is narrowed, the developing agent clogs in the hose. Consequently, a problem such that the developing agent overflows around the funnel into the apparatus occurs. In a printer, a copying machine, a facsimile, or the like, it is strongly requested to eject the developing agent at a high speed. In order to realize the high ejecting speed, rotational speeds of the magnet roller and the stirring screw are raised. However, since a large amount of developing agent is dropped to the funnel in association with an increase in speed, the developing agent clogs in the funnel and the hose and a problem of the overflow of the developing agent around the funnel into the apparatus occurs.